原行星盘中的尘埃-尘埃碰撞充电和闪电
Dust-Dust Collisional Charging and Lightning in Protoplanetary Discs
摘要：
我们研究了尘埃-尘埃碰撞充电在原行星盘中的作用。我们表明，尘埃-尘埃碰撞充电成为一个重要的过程，在确定尘埃和气体的电荷状态，如果有灰尘增强和/或灰尘是蓬松的，使尘埃表面积每盘体积局部增加。利用通用图形处理器（GPGPU）和{ \sc cuda}编程语言，求解了不同圆盘环境和尘埃数密度$η$的电荷平衡方程。我们发现随着尘埃数密度$η$的增加，电荷分布经历了四个阶段。在这些阶段之一中，由尘埃运动引起的静电场$E$增加为$E \propto η^4$。结果，发生宏观放电，例如在$η= 70$（以最小质量太阳星云（MMSN）值为单位，考虑两组具有半径$10^{-2}\unit{cm}$、$10^{2}\unit{cm}$的蓬松尘埃）。我们提出了一个模型，描述的电荷交换过程中的光盘作为一个电路。本文导出了闪电的临界尘埃数密度随尘埃参数变化的解析公式。我们估计了这种放电（“闪电”）的总能量、强度和事件比率。讨论了利用天文低频（{ \em ALF}）波、{ \em IR}、{\em UV}谱线和高能γ射线观测原行星盘中闪电和精灵放电的可能性。我们还讨论了闪电对球粒加热、星子生长和盘的磁旋转不稳定性的影响。
英文摘要：
We study the role of dust-dust collisional charging in protoplanetary discs. We show that dust-dust collisional charging becomes an important process in determining the charge state of dust and gas, if there is dust enhancement and/or dust is fluffy, so that dust surface area per disc volume is locally increased. We solve the charge equilibrium equations for various disc environments and dust number density $η$, using general purpose graphic processors (GPGPU) and {\sc cuda} programming language. We found that as dust number density $η$ increases, the charge distribution experience four phases. In one of these phases the electrostatic field $E$ caused by dust motion increases as $E \propto η^4$. As a result, macroscopic electric discharge takes place, for example at $η= 70$ (in units of minimum-mass solar nebula (MMSN) values, considering two groups of fluffy dust with radii $10^{-2}\unit{cm}$, $10^{2}\unit{cm}$). We present a model that describes the charge exchange processes in the discs as an electric circuit. We derive analytical formulae of critical dust number density for lightning, as functions of dust parameters. We estimate the total energy, intensity and event ratio of such discharges (`lightning'). We discuss the possibility of observing lightning and sprite discharges in protoplanetary discs by Astronomically Low Frequency ({\em ALF}) waves, {\em IR} images, {\em UV} lines, and high energy gamma rays. We also discuss the effects of lightning on chondrule heating, planetesimal growth and magnetorotational instability of the disc.
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